The present invention is directed to an interface means having amplification and attenuation elements as well as different signalization detectors between a bidirectional transmission channel having analog signals and a signal process-codec filter having a four-wire input for matching the line signalizations to interface messages of a digital communication system.
Such an interface means represents the connecting element between the signal process-codec filter and the transformer of a link between private branch exchanges or, respectively, between private branch exchanges and a public exchange. This interface means must meet a number of functions. For supporting the signal processor-codec filter, such functions are, for example, amplifying or, respectively, attenuating voice signals, and setting up a negative feedback for promoting the formation of an input impedance. In addition, the interface means must be in a position to filter out and to acquire call charge pulses as well as to suppress the call charge pulses in the direction toward the signal processor-codec filter. Further, ringing signals and cleardown messages must be recognized. The full duplex capability of the overall transmission channel cannot be limited and the interface means must be disconnectible in a standby mode. Signalization voltages of a maximum of 12 volts must be capable of being effectively processed for the call charges with a frequency of 12 kHz or, respectively, 16 kHz and 90 V must be capable of being effectively processed for the cleardown voltage in the frequency range&lt;60 Hz and voice signal voltages below 1.1 V must be capable of being effectively processed in the voice-band (0.3 through 3.4 kHz).